Sensitivity to oscillation with a sterile fourth generation neutrino from ultralow threshold neutrino-nucleus coherent scattering

Bhaskar Dutta, Yu Gao, Andrew Kubik, Rupak Mahapatra, Nader Mirabolfathi, Louis E. Strigari, and Joel W. Walker

Phys. Rev. D 94, 093002 – Published 14 November 2016

Abstract

We discuss prospects for probing short-range sterile neutrino oscillation using neutrino-nucleus coherent scattering with ultralow energy ( $\sim 10 - 100 eV$ ) recoil threshold cryogenic Ge detectors. The analysis is performed in the context of a specific and contemporary reactor-based experimental proposal, developed in cooperation with the Nuclear Science Center at Texas A&M University, and references developing technology based upon economical and scalable detector arrays. The baseline of the experiment is substantially shorter than existing measurements, as near as about 2 m from the reactor core, and is moreover variable, extending continuously up to a range of about 10 m. This proximity and variety combine to provide extraordinary sensitivity to a wide spectrum of oscillation scales, while facilitating the tidy cancellation of leading systematic uncertainties in the reactor source and environment. With 100 eV sensitivity, for exposures on the order of $200 kg \cdot y$ , we project an estimated sensitivity to first and fourth neutrino oscillation with a mass gap $Δ でるた m^{2} \sim 1 {eV}^{2}$ at an amplitude $\sin^{2} 2 θ しーた \sim 10^{- 1}$ , or $Δ でるた m^{2} \sim 0.2 {eV}^{2}$ at unit amplitude. Larger exposures, around $5000 kg \cdot y$ , together with 10 eV sensitivity are capable of probing more than an additional order of magnitude in amplitude.

Received 7 December 2015

DOI:https://doi.org/10.1103/PhysRevD.94.093002

Physics Subject Headings (PhySH)

Neutrino interactions Neutrino oscillations Nucleus-neutrino interactions

Sterile neutrinos

Neutrino detection

Particles & Fields

Authors & Affiliations

Bhaskar Dutta¹, Yu Gao¹, Andrew Kubik¹, Rupak Mahapatra¹, Nader Mirabolfathi¹, Louis E. Strigari¹, and Joel W. Walker²

¹Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843-4242, USA
²Department of Physics, Sam Houston State University, Huntsville, Texas 77341, USA

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Vol. 94, Iss. 9 — 1 November 2016

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Images

Figure 1
Fractional deviation from expected SM $CE ν にゅー NS$ event rates in Ge due to electron antineutrino oscillation with a sterile fourth flavor. Separate basis curves ${γ がんま}^{i}$ are displayed for nine binned windows in the nuclear kinetic recoil energy deposition. A tenth (bold, dashed) curve demonstrates the cumulative unbinned event deviation over all recoils above 10 eV. For a given energy band, values approaching one indicate more full depletion relative to the SM, whereas values nearer to zero indicate more marginal depletion. The vertical axis is inversely rescaled by the amplitude factor $\sin^{2} 2 {θ しーた}_{14}$ , and predictions for any targeted amplitude may be immediately read off by replacing the upper limit (1.0) with the applicable value. The horizontal axis indicates the product of the distance from core in meter units and the mass-square difference $Δ でるた m_{14}^{2}$ in units of ${eV}^{2}$ . For example, at a gap of $1 {eV}^{2}$ , this axis is read literally in meters, whereas the outer scale bound at 100 would correspond instead to 10 m for $Δ でるた m_{14}^{2} = 10 {eV}^{2}$ . The presented binning is merely suggestive and will ultimately be strongly dependent upon precise calibration of the nuclear response function at low energies.
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Figure 2
Figures depict contours in the ${χ かい}^{2}$ statistical significance, specifically $S / \sqrt{B}$ , where the signal $S$ corresponds to an event deficit attributable to oscillation with a sterile fourth generation neutrino relative to the background expectation $B$ for the SM electron antineutrino $CE ν にゅー NS$ event rate in Ge. Scale-invariant projections are made in terms of the mass gap $Δ でるた m_{14}^{2} {eV}^{2}$ and the amplitude $\sin^{2} 2 {θ しーた}_{14}$ , as a product or quotient with the experimental baseline $L m$ , respectively, and times the square root of exposure in the latter case. At unit distance, exposure time and mass these factors drop out, and the axes may be read traditionally. The detector recoil energy is unbinned in this analysis. The left- and right-hand panel integrates all recoils above the more conservative and more optimistic thresholds of 100 and 10 eV, respectively.
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Figure 3
Phase-1 prospective limit of ${ν にゅー}_{e} - {ν にゅー}_{s}$ mixing parameters with 100 kg Ge detector mass and 2 yr effective exposure at a sample distance of 2 (left) or 5 m (right) from the reactor. A minimum recoil threshold of 100 eV is adopted. Contours are shown in the ${χ かい}^{2}$ statistical significance, specifically $S / \sqrt{B}$ , where the signal $S$ corresponds to the oscillation event deficit and the background $B$ sums the SM electron antineutrino $CE ν にゅー NS$ event rate together with a postulate for the unified reactor plus cosmic, etc., event rate. This additional background component is modeled with a strength of 100 or 10 dru at the near and far positions, respectively. Global 95% short-baseline (blue dashed curve) and ${ν にゅー}_{e}$ disappearance (red solid curve) fits [39] and projected SOX [19] and $Solar + Kamland$ [40] limits are plotted for rough comparison.
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Figure 4
Phase-2 prospective limit of ${ν にゅー}_{e} - {ν にゅー}_{s}$ mixing parameters with 1000 kg Ge detector mass and 5 yr effective exposure at a sample distance of 2 (left) or 5 m (right) from the reactor. A minimum recoil threshold of 10 eV is adopted. The additional background component is modeled with a strength of 10 or 1 dru at the near and far positions, respectively. Contours and overlays are as described in Fig. 3.
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